Technical Field
The present invention relates to an image forming apparatus, and in particular to an electrophotographic image forming apparatus that forms images electrophotographically.
Description of the Related Art
Although the photoconductive image bearer and developing roller employed in an electrophotographic image forming apparatus are cylindrical, this cylindrical shape is not perfect. These imperfections cause density variation in the toner image during image formation.
A charging bias applied to the charging roller and the charging bias applied to the developing roller are corrected to compensate for these imperfections in the image bearer and the developing roller, thereby suppressing image density variation.
However, adjustment of the charging bias to compensate for the effect of imperfections in parts such as the image bearer and the developing roller is generally insufficient, resulting in abnormal images generated due to density variation in the toner image keyed to the rotary cycle of the charging roller.
It is possible to employ a structure that reduces the charge variation generated due to fluctuation in the size of a gap between the image bearer and the charging roller, or a structure in which a rotational speed of the charging roller is variable. The problem, however, is that such imperfections in the charging roller include not only the shape of the charging roller but also the electrical resistance thereof.
Further, having to provide a structure to rotate the charging roller and another structure to detect a gap between the image forming apparatus and the charging roller to control the rotational speed of the charging roller complicates the image forming apparatus.